To enable encrypted data which are transmitted by means of broadcast radio signals and which can be used only in return for a fee, it is known practice to provide the user with a license key. This can either be input manually as an access code or can be provided as a key record on a data storage medium for the purpose of executing a decryption algorithm.
Thus, by way of example, in order to use pay televisions, the users are provided with access authorization memory cards which, in conjunction with a video data decoder, allow an encrypted broadcast radio program to be decrypted.
To protect data and software which are stored and sold on a data storage medium against unauthorized use when unauthorized pirate copies have been produced, it is known practice to produce an access code comprising a license key and a license number stored on the data storage medium. Alternatively, the license number may be requested from the data supplier by telephone or using a computer network by indicating the license key which is printed on the data storage medium. The access code is then stored and allows the installed data, for example in the form of software, once enabled, to be used without requiring renewed authorization.
With knowledge of the license key and possibly of the enabling code, however, it is also possible for any third party to use the data in conjunction with an unauthorized copy of the data on a copy data storage medium.
It is also known practice to calculate the access code from a combination comprising a license key with the serial number of the data processing device processing the data. This has the drawback for the user that the inherently authorized data storage medium can be used only in conjunction with a single data processing device which the user stipulates when the data are enabled the first time.